Aplidine has a cyclic structure with a sidechain, as follows:

The didemnins form a class of cyclic depsipeptides which have been isolated from various species of the Trididemnum genus (Rinehart, Jr. et al. J., Am. Chem. Soc, 103, 1857-59 (1981), Rinehart, Jr. et al. Science, 212, 933-935 (1981) with potent antitumoral and antiviral activities. Among them, aplidine is one of the most antitumoral active natural didemnins. Description of the isolation and antitumoral activity of Aplidine is provided in U.S. Pat. No. 5,834,586 patent.
A number of synthetic or natural analogs of Aplidine have been described (Rinehart, Jr. et al. J. Med. Chem, 1996, 39, 2819-2834) that include different modifications in the side chain, but preserving the same macrocyclic structure.
Recently have been described a related structure of didemnins called Tamandarins (Fenical, W et al., J. Org. Chem., 2000, 65, 782-792) which were isolated from an unidentified ascidian of the family didemnidae. These molecules were found to differ only by the presence of hydroxyisovaleric acid (Hiv3), instead of the hydroxyisovalerylpropionic acid (Hip3). They have been described as highly active antiviral, antitumor and immunosuppresive peptides.
